1. Field of the Invention
The present invention relates to a reciprocating compressor. In particular, the present invention relates to a lubricating device of a reciprocating compressor which reduces noise generated when lubricating oil is discharged and prevents the lubricating oil from flowing back.
2. Description of the Related Art
Generally, compressors can be divided into different categories including a rotary compressor, a reciprocating compressor, a scroll compressor, and etc. based upon the method utilized therein for compressing a fluid.
FIG. 1 is a sectional view of a reciprocating compressor in accordance with the conventional art.
The reciprocating compressor according to the conventional art comprises a hermetically-sealed case 106 to which a suction pipe 102 and a discharge pipe 104 are connected, a driving unit 108 provided in the case 106 for generating a reciprocating force, a compressing unit 110 for compressing a fluid by application of the reciprocating force generated by the driving unit 108, and a lubricating device for supplying lubricating oil to each frictionally-contacting part of the compressor.
The driving unit 108 includes an outer stator 116 of a cylindrical shape arranged between a middle frame 112 and a rear frame 114 an inner stator 118 spaced by a predetermined air gap from an inner circumferential surface of the outer stator 116. A coil 120 to which power from a power source is applied is coiled or wound about an inner part of the outer stator 116. A magnet 122 arranged between the outer stator 116 and the inner stator 118 with a predetermined interval for linearly reciprocating when power is applied to the coil 120.
The magnet 122 is fixed to an outer circumferential surface of a magnet holder 124 with a same interval, and the magnet holder 124 is connected to a piston 126 of the compressing unit 110. The piston 126 is connected to a spring supporter 128.
A first spring 130 and a second spring 132 are respectively arranged at both sides of the spring supporter 128 and a front frame 134 on one hand, and the middle frame 112 on the other hand, thereby providing an elastic force when the piston 126 moves forward or backward.
The compression unit 110 includes the piston 126 connected to the magnet holder 124 for linearly reciprocating; a cylinder 136 into which the piston 126 is slidingly-inserted for forming a predetermined compression space 142; a suction valve 140 mounted in front of the piston 126 for opening/closing a fluid passage 138 formed at the piston 126; and a discharge valve assembly mounted at the front frame 134 for opening/closing the flow of fluid to be discharged.
The discharge valve assembly includes: a discharge valve 144 tightly pressed into contact with a front surface of the cylinder 136 and capable of being opened and closed; a discharge cover 146 engaged to a front of the cylinder 136 and connected to the discharge pipe 104 through which a fluid is discharged; and a spring 148 arranged between an inner side of the discharge cover 146 and the discharge valve 144 for providing a predetermined elastic force to the discharge valve 144.
The lubricating device, as shown in FIGS. 2 and 3, supplies lubricating oil contained in a lower portion of the case 106 to a sliding part or area between the cylinder 136 and the piston 126. The lubricating device includes: a pumping unit 150 mounted at a lower side of the front frame 134 for pumping lubricating oil; a supply passage 152 formed at a front of the front frame 134 for supplying the lubricating oil pumped by the pumping unit 150; a lubricating oil suction hole 154 connected to the supply passage 152 for taking-in lubricating oil and conveying the oil into the sliding part between the cylinder 136 and the piston 126; and a discharge hole 156 formed at an opposite side of the suction hole 154 at the front frame 134 for discharging the lubrication oil which has finished a lubrication operation back into the compressor case.
An engaging portion 162 to which the discharge cover 146 is bolt-engaged protrudes from the front of the front frame 134, and an air hole 160 for passing gas towards inner and outer sides of the front frame 134 is formed therein and extends along a circumferential direction of the engaging portion 162 so that a resistance may not be generated when the piston 126 reciprocates.
Operations of the lubricating device will be explained. As shown in FIG. 3, when the pumping unit 150 is operated, the lubricating oil contained in the lower portion of the case 106 is pumped to the supply passage 152, and supplied to the sliding part (i.e., surface) between the cylinder 136 and the piston 126 through the suction hole 154, thereby performing a lubrication operation. Then, the lubricating oil which finished the lubrication operation is discharged to an inside of the case 106 through the discharge hole 156, and is collected at the lower portion of the case 106.
However, in the lubricating device according to the conventional art, since the lubrication oil is discharged in a mixed state with a fluid (e.g., air) through the discharge hole 156, foam is generated. Accordingly, if the lubrication oil having the foam is discharged, the foam bursts and noise is generated.
Also, since the lubrication oil is discharged through the discharge hole 156 with a high pressure, the lubrication oil collides with an inner wall of the case 106 and generates noise.
Additionally, if the lubrication oil discharged through the discharge hole 156 and then sucked into the air hole 160 formed at the front of the front frame 134, a flow resistance of the fluid is generated when the piston 126 reciprocates, thereby lowering a performance of the compressor.